Pen type drug delivery devices have application where regular injection by persons without formal medical training occurs. This may be increasingly common among patients having diabetes where self-treatment enables such patients to conduct effective management of their disease.
There are basically two types of pen type delivery devices: resettable devices (i.e., reusable) and non-resettable (i.e., disposable). These types of pen delivery devices (so named because they often resemble an enlarged fountain pen) are generally comprised of three primary elements: (i) a cartridge section that includes a cartridge often contained within a housing or holder; (ii) a needle assembly connected to one end of the cartridge section; and (iii) a dosing section connected to the other end of the cartridge section. A cartridge (often referred to as an ampoule) typically includes a reservoir that is filled with a medication (e.g., insulin), a movable rubber type bung or stopper located at one end of the cartridge reservoir, and a top having a pierceable rubber seal located at the other, often necked-down, end. A crimped annular metal band is typically used to hold the rubber seal in place. While the cartridge housing may be typically made of plastic, cartridge reservoirs have historically been made of glass.
The needle assembly is typically a replaceable double-ended needle assembly. Before an injection, a replaceable double-ended needle assembly is attached to one end of the cartridge assembly, a dose is set, and then a dose is administered. Such removable needle assemblies may be threaded onto, or pushed (i.e., snapped) onto the pierceable seal end of the cartridge assembly.
The dosing section or dose setting mechanism is typically the portion of the pen device that is used to set a dose. During an injection, a spindle contained within the dose setting mechanism presses against the bung or stopper of the cartridge. This force causes the medication contained within the cartridge to be injected through the attached needle assembly. After an injection, as generally recommended by most drug delivery device and/or needle assembly manufacturers and suppliers, the needle assembly is removed and discarded.
The dose setting mechanism further comprises a number sleeve which is used to display the dialled dose. This number sleeve has dose numbers on the external surface so that the dose number dialled is visible through a window, aperture or lens in the housing. The number sleeve must be prevented from being dialled out beyond a pre-set rotational stop distance so that it does not disengage from the housing.
It is therefore an object of the present invention to provide a dose setting mechanism which meets above mentioned needs. It is another object of the present invention to specify a easy and cost-effective method of assembling such dose setting mechanism.